1. Field of the Invention
This invention relates to a dispersing agent for a pigment (hereinafter often xe2x80x9cpigment-dispersing agentxe2x80x9d) which is to improve the dispersibility of a pigment in the process of producing coating materials, inks, toners or resin molded products, and a pigment-dispersion composition which contains the dispersing agent. This invention also relates to a toner for forming a toner image in an image-forming process such as electrophotography or electrostatic printing or a image-forming process carried out by a toner-jet method, and a process for producing such a toner.
2. Related Background Art
In the manufacture of coating materials, inks, toners or resin molded products, pigment-dispersing agents have effectively been utilized as additives for making pigments have small particle diameter so as to sufficiently bring out the performance required as coloring materials (such as coloring power, transparency and luster).
In order for a pigment-dispersing agent to exhibit its function, the agent is required to have a chemical structure that it is strongly adsorptive on the pigment in the molecule and a chemical structure that it has affinity for mediums, solvents and resins used in dispersing the pigment and can be a steric hindrance for preventing re-agglomeration of the pigment. As a dispersing agent for phthalocyanine pigments or carbon black, a derivative of phthalocyanine coloring matter is used. In order to make the pigment have general-purpose properties for various mediums, solvents and resins, it is common to separately add an agent having adsorptivity on the pigment and a resin material which has affinity for mediums, solvents and resins and can be a steric hindrance, and make these combine with each other by acid-base mutual action to bring out the function as the pigment-dispersing agent.
However, when such a two-component type dispersing agent is used, it is necessary to prepare a pigment-dispersion composition under such conditions that the bond attributable to the acid-base which keeps the both combined with each other does not break. Especially when the pigment is dispersed in an aqueous medium, attention must be paid also to the pH of water or mediums and the functional group of the resin to be added. Even when the pigment is dispersed in the state the both have dissociated, the state of dispersion to a certain extent can be achieved on account of the action of polar groups of a phthalocyanine derivative. It, however, may come into question that the pigment re-agglomerates in post steps of drying, shaping, polymerization reaction and so forth or that the pigment migrates to particle surfaces because of the presence of polar groups.
Meanwhile, toner particles used in printers and copying machines are fine particles formed chiefly of (i) a resin, (ii) a colorant such as a magnetic material, carbon black, a dye or a pigment and (iii) a wax, and have particle diameters usually ranging from 6 to 30 xcexcm. Toner particles are commonly produced by mixing and melting a colorant comprised of a dye or pigment or a magnetic material in a thermoplastic resin to disperse the colorant uniformly in the thermoplastic resin, followed by fine pulverization and classification to obtain toner particles having a desired particle diameter. This method is relatively stable as a technique, and enables relatively easy management of materials and production steps. Since, however, the particle diameter of toner particles depends on the mechanical pulverization of resins, an attempt to make their particle diameter small to an average particle diameter of 6 xcexcm or less results in a low yield. This is because, in view of an attribute that the charge quantity increases with a decrease in particle diameter when a toner having toner particles is electrostatically charged by means of a triboelectric charging member, its particle size distribution must be made sharp in order for the toner to be uniformly charged and this makes it necessary to remove finer power and coarse powder in a large quantity in the step of classification.
In recent years, as a method having overcome the above problem, a method of producing toner particles by polymerization (e.g., a method of producing toner particles by suspension polymerization) is proposed. Such a method is disclosed in, e.g., Japanese Patent Publication No. 36-10231 and No. 51-14895 and Japanese Patent Application Laid-open No. 53-17735, No. 53-17736 and No. 53-17737. This method is a method in which materials to be included into toner particles, such as a colorant (e.g., a magnetic material or carbon black), a charge control agent and a release agent (e.g., a wax) are dissolved or dispersed in a polymerizable monomer optionally together with a polymerization initiator and a dispersing agent to prepare a polymerizable composition, which is then dispersed in an aqueous medium containing a dispersion stabilizer, by means of a dispersion apparatus to form fine particles, and the polymerizable monomer in the fine particle is polymerized and then solidified to obtain toner particles having any desired particle diameter and composition. This method has not any pulverization step, and is expected to bring about the effect of energy saving, improvement in process yield and cost reduction. On the other hand, depending on production conditions such as the state of stirring and the size of production scale, toner particles whose particle size distribution has varied to have a relatively broad particle size distribution are obtained in many cases, and the step of classification must be carried out in many cases in order to regulate them to have a desired particle size distribution required to obtain high-quality and highly minute toner images.
As a method of producing toner particles by dispersion polymerization promising much sharper particle size distribution, a method is available which makes use of dispersion polymerization proposed in Japanese Patent Publication No. 6-17073 and Japanese Patent Application Laid-open No. 61-18965, No. 61-18966, No. 61-228458 and No. 62-73276. This is a method of producing toner particles with uniform particle size distribution by initiating polymerization reaction by heat or light, from a uniform system in which a polymeric dispersing agent, a polymerizable monomer, a polymerization initiator, a colorant, a charge control agent and so forth have been dissolved or dispersed, to form those which serve as nuclei of toner particles, and allowing the particles to grow individually. The dispersion polymerization is regarded as a reliable method of producing monodisperse particles of about 1 to 10 xcexcm in particle diameter. Because of their very sharp particle size distribution, a toner having such toner particles can also have a sharp charge quantity distribution, and, compared with those produced by other methods, has superior dot reproducibility in development, fidelity of transfer and fixing performance. The dispersion polymerization, however, has a problem that, when used as a method of producing toner particles, the colorant such as a pigment, which tends to be insoluble in the reaction system, may enter the interiors of particles with difficulty.
In recent years, in order to overcome this problem, it is proposed in Japanese Patent No. 2,633,383 (corresponding to U.S. Pat. No. 5,124,226) to treat the surfaces of pigment particles so that the pigment can be incorporated into the toner particles with ease. According to this publication, it is disclosed that toner particles with uniform particle diameter which contain the pigment in the interiors of toner particles can be obtained using as a pigment-dispersing agent a compound having radical-polymerizable groups. In reality, however, the situation is that the pigment can slightly be incorporated into the toner particles. Accordingly, it is sought to further incorporate the pigment into toner particles to more improve coloring efficiency.
In addition, where toner particles are colored in the conventional method, the pigment is incorporated in so poor an efficiency at the initial stage of polymerization reaction that the toner particles tend to be those in which the pigment has mostly adhered to the toner particle surfaces. Thus, depending on the type of the pigment, the surfaces of toner particles have so poor environmental properties as to enable charge control with difficulty in some cases.
An object of the present invention is to provide a dispersing agent for a pigment, a pigment-dispersion composition, a toner and a toner production process which have solved the above problems.
Another object of the present invention is to provide a dispersing agent for a pigment, which can finely disperse the pigment with ease.
Still another object of the present invention is to provide a pigment-dispersion composition which can stably maintain the state of dispersion even in various post steps.
A further object of the present invention is to provide a toner having a sharp particle size distribution and a superior coloring power, and a process for producing such a toner.
A still further object of the present invention is to provide a monodisperse toner having a superior coloring efficiency, and a process for producing such a toner.
A still further object of the present invention is to provide a monodisperse toner having a superior charging performance, and a process for producing such a toner.
A still further object of the present invention is to provide a toner having toner particles in which a pigment has finely been dispersed to make the toner have superior coloring power and transparency, and a process for producing such a toner.
A still further object of the present invention is to provide, in a process for producing toner particles by polymerization making use of an aqueous medium, a toner having toner particles to the surfaces of which the colorant does not migrate and which have superior charging performance and environmental stability, and a process for producing such a toner.
To achieve the above objects, the present invention provides a dispersing agent for a pigment, comprising a compound represented by the following Formula (1) or (2). 
wherein at least one of R1, R2, R3 and R4 represents a substituent X: 
where a substituent Y represents an oligomer unit or a polymer unit,
and others each represent a hydrogen atom. 
wherein at least one of R1, R2, R3 and R4 represents a substituent X: 
where a substituent Y represents an oligomer unit or a polymer unit,
and others each represent a hydrogen atom; and M represents a divalent metal, a tri- or tetravalent substituted metal, or an oxy-metal.
The present invention also provides a pigment-dispersion composition comprising a pigment, a dispersing agent for a pigment, and a medium, wherein the dispersing agent is a compound represented by the following Formula (1) or (2). 
wherein at least one of R1, R2, R3 and R4 represents a substituent X: 
where a substituent Y represents an oligomer unit or a polymer unit,
and others each represent a hydrogen atom. 
wherein at least one of R1, R2, R3 and R4 represents a substituent X: 
where a substituent Y represents an oligomer unit or a polymer unit,
and others each represent a hydrogen atom; and M represents a divalent metal, a tri- or tetravalent substituted metal, or an oxy-metal.
The present invention still also provides a toner comprising a binder resin and a pigment, wherein the pigment has been treated with a compound represented by the following Formula (1) or (2). 
wherein at least one of R1, R2, R3 and R4 represents a substituent X: 
where a substituent Y represents an oligomer unit or a polymer unit,
and others each represent a hydrogen atom. 
wherein at least one of R1, R2, R3 and R4 represents a substituent X: 
where a substituent Y represents an oligomer unit or a polymer unit,
and others each represent a hydrogen atom; and M represents a divalent metal, a tri- or tetravalent substituted metal, or an oxy-metal.
The present invention further provides a process for producing a toner containing toner particles; the process comprising;
introducing a monomer composition containing at least a polymerizable monomer and a pigment, into a medium containing at least an organic solvent and a polymeric dispersion stabilizer;
dissolving at least the polymerizable monomer in the medium;
polymerizing the monomer; and
precipitating from the medium a polymer formed by the polymerization to produce toner particles containing the pigment;
wherein;
the pigment has been treated with a compound represented by the following Formula (1) or (2). 
wherein at least one of R1, R2, R3 and R4 represents a substituent X: 
where a substituent Y represents an oligomer unit or a polymer unit,
and others each represent a hydrogen atom. 
wherein at least one of R1, R2, R3 and R4 represents a substituent X: 
where a substituent Y represents an oligomer unit or a polymer unit,
and others each represent a hydrogen atom; and M represents a divalent metal, a tri- or tetravalent substituted metal, or an oxy-metal.
The present invention is characterized in that the pigment-dispersing agent has a structure wherein a phthalocyanine type molecular skeleton which is adsorptive on the pigment and an oligomer unit or polymer unit which prevents re-agglomeration of the pigment to bring out the effect of dispersion are covalently bonded, and has affinity for a medium or a solvent.
The pigment-dispersing agent of the present invention has the structure of the above Formula (1) or (2). In Formula (1) or (2), at least one of R1, R2, R3 and R4 is the substituent X. As to the number of the substituent X, one or two of R1 to R4 may preferably be the substituent(s) X because the substituent X may on the one hand strengthen the affinity for a medium or a solvent described later, and may on the other hand inhibit the adsorptivity on the pigment. Other substituents are each a hydrogen atom (H). Also, the metal M in Formula (2) is a divalent metal, a tri- or tetravalent substituted metal, or an oxy-metal, which may include, e.g., metals such as Cu, Al, Fe, Co, Ni, Zn, Mg, Mn and Pb; metal chlorides such as TiCl2 and SnCl2; and metal oxides such as TiO and MnO.
The substituent Y, which constitutes the substituent X, is an oligomer or a polymer, and may preferably have good affinity for the medium or solvent and for a resin contained in the medium or solvent.
As the substituent Y that can be used in the present invention, a known oligomer or polymer unit may be used as the substituent. For example, it may include styrene oligomer, polystyrene, acrylic acid oligomer, polyacrylic acid, methacrylic acid oligomer, polymethacrylic acid, acrylate oligomer, polyacrylate, methacrylate oligomer, polymethacrylate, ester oligomer, polyester, vinyl ether oligomer, polyvinyl ether, vinyl methyl ether oligomer, polyvinyl methyl ether, vinyl alcohol oligomer, polyvinyl alcohol, vinyl butyral oligomer, and polyvinyl butyral. It may further include copolymers formed of a plurality of monomers used to form any of these polymers. The polymer unit is preferably a polystyrene unit, a styrene-acrylate copolymer unit, a styrene-methacrylate copolymer unit, a styrene-acrylic acid copolymer unit or a styrene-methacrylic acid copolymer unit.
The solvent that can be used in the present invention is one determined taking account chiefly of its affinity for the substituent Y. Stated specifically, the solvent may include water; alcohols such as methyl alcohol, ethyl alcohol, modified ethyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, sec-butyl alcohol, tert-amyl alcohol, 3-pentanol, octyl alcohol, benzyl alcohol and cyclohexanol; ether alcohols such as methyl cellosolve, cellosolve, isopropyl cellosolve, butyl cellosolve, diethylene glycol and monobutyl ether; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate, butyl acetate, ethyl propionate and cellosolve acetate; hydrocarbons such as hexane, octane, petroleum ether, cyclohexane, benzene, toluene and xylene; halogenated hydrocarbons such as carbon tetrachloride, trichloroethylene and tetrabromoethane; ethers such as ethyl ether, dimethyl glycol and trioxane tetrahydrofuran; acetals such as methylal and diethyl acetal; organic acids such as formic acid, acetic acid and propionic acid; and sulfur- or nitrogen-containing organic compounds such as nitropropene, nitrobenzene, dimethylamine, monoethanolamine, pyridine, dimethyl sulfoxide and dimethyl formamide. Two or more of any of these liquid mediums or solvents may also be used in the form of a mixture.
The liquid medium or solvent may also more preferably be a polymerizable monomer.
The polymerizable monomer that can be used in the present invention is an addition polymerization or condensation polymerization type monomer. It may preferably be an addition polymerization type monomer. Such a monomer may specifically include styrene; styrene derivatives such as o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene and p-n-dodecylstyrene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; unsaturated polyenes such as butadiene and isoprene; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide and vinyl iodide; vinyl esters such as vinyl acetate, vinyl propionate and vinyl benzoate; xcex1-methylene aliphatic monocarboxylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; acrylic esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate and phenyl acrylate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and isobutyl vinyl ether; vinyl ketones such as methyl vinyl ketone, hexyl vinyl ketone and methyl isopropenyl ketone; vinylnaphthalenes; and acrylic acid derivatives such as acrylonitrile, methacrylonitrile and acrylamide.
As a process for producing the pigment-dispersing agent of the present invention, any known method may be used. A method is available in which the reactivity of hydrogen of the four benzene nuclei in the phthalocyanine skeleton is utilized to effect chlorination or sulfonation to synthesize a derivative. More preferably, a carboxylated phthalocyanine can readily be synthesized using trimellitic anhydride and phthalic anhydride as materials of the carboxylated phthalocyanine. As to such a carboxylic group, a halogen can readily be replaced by an alkyl group by the Friedel-Crafts reaction through an acid halide. For example, to introduce a polystyrene unit (group), the hydrogen at the para-position of a phenyl group can readily be substituted in the presence of anhydrous aluminum chloride.
In the pigment-dispersion composition of the present invention, components other than the pigment-dispersing agent of the present invention may include a pigment, a resin, a dispersing agent, other additives, a liquid medium and a solvent. As a process for producing the pigment-dispersion composition, any known method may be used. For example, the pigment-dispersing agent and optionally the resin may be dissolved or dispersed in the liquid medium or solvent, and powder of a pigment may be added little by little with stirring to make it fit well to the liquid medium or solvent. Mechanical shear force is further applied by means of a dispersion machine such as a ball mill or a paint shaker, a dissolver, an attritor, a sand mill or a high-speed mill to make the pigment-dispersing agent adsorbed on the surfaces of particles of the pigment, and the pigment can stably finely be dispersed.
As a process for producing the toner of the present invention, any known method may be used, provided that the pigment-dispersing agent of the present invention is used in the step of dispersing the pigment.
In the case of a pulverization toner, a pigment-dispersion paste as the pigment-dispersion composition is mixed with the resin as a toner binder together with other additives, and the mixture obtained is melt-kneaded by heat and mechanical shear force. The kneaded product thus obtained is pulverized, followed by the step of classification to obtain the toner.
In a process for producing a toner by polymerization making use of an aqueous medium, in particular, a process for producing a toner by suspension polymerization, as the pigment-dispersion composition a pigment-dispersion paste making use of a polymerizable monomer may be introduced into an aqueous medium together with a polymerization initiator, and the polymerization reaction is caused by light or heat to polymerize the polymerizable monomer to obtain toner particles.
In the case of dispersion polymerization, the pigment-dispersing agent and optionally a polymeric stabilizer and other additives may be dissolved or dispersed in a polymerizable monomer, and powder of a pigment added is little by little with stirring to make it fit well to the polymerizable monomer. Mechanical shear force is further applied by means of a dispersion machine such as a ball mill or a paint shaker, a dissolver, an attritor, a sand mill or a high-speed mill to make the pigment-dispersing agent adsorbed on the surfaces of particles of the pigment, and the pigment is stably finely dispersed. The dispersion obtained is mixed with a reaction medium having an organic solvent and a polymeric dispersion stabilizer, and a polymerization initiator is added thereto. Then the polymerization reaction is caused by light or heat with gentle stirring, and a polymer formed from the polymerizable monomer is precipitated to obtain polymerization toner particles.
In the case of the dispersion polymerization, what is effective as the substituent Y in the above Formulas (1) and (2) is a styrene oligomer, a styrene polymer, an acrylic oligomer, an acrylic polymer, an ester oligomer, an ester polymer, or a copolymer of monomers for any of these. It may preferably be one having affinity for the organic solvent, the reaction medium containing a polymeric dispersion stabilizer and the polymerizable monomer. The substituent Y may preferably have a number-average molecular weight of from 300 to 30,000, which may preferably be equal to or less than the number-average molecular weight of the polymeric dispersion stabilizer. One having a number-average molecular weight smaller than 300 is not preferable because the effect of dispersing the pigment may be obtained with difficulty. If it has a number-average molecular weight larger than 30,000, the adsorptivity of the pigment-dispersing agent on the pigment may be inhibited to bring about a low dispersion effect, and also the pigment can not well be incorporated into toner particles, resulting in a low coloring power of the toner.
The polymerizable monomer that can be used in the process for production the toner of the present invention is an addition polymerization or condensation polymerization type monomer. It may preferably be an addition polymerization type monomer. The addition polymerization type monomer may specifically include styrene; styrene derivatives such as o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene and p-n-dodecylstyrene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; unsaturated polyenes such as butadiene and isoprene; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide and vinyl iodide; vinyl esters such as vinyl acetate, vinyl propionate and vinyl benzoate; xcex1-methylene aliphatic monocarboxylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; acrylic esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate and phenyl acrylate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and isobutyl vinyl ether; vinyl ketones such as methyl vinyl ketone, hexyl vinyl ketone and methyl isopropenyl ketone; N-vinyl compounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole and N-vinylpyrrolidone; vinylnaphthalenes; and acrylic or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile and acrylamide.
As the pigment that can be used in the present invention, any known pigment may be used. In particular, color pigments such as phthalocyanine pigments and carbon black may preferably be used. The pigment may preferably be added in an amount of from 3 to 20 parts by weight based on 100 parts by weight of the polymerizable monomer.
The solvent that can be used in the process for production the toner of the present invention is one determined taking account chiefly of the solubility of the monomer and polymer. Stated specifically, the solvent may include water; alcohols such as methyl alcohol, ethyl alcohol, modified ethyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, sec-butyl alcohol, tert-amyl alcohol, 3-pentanol, octyl alcohol, benzyl alcohol and cyclohexanol; ether alcohols such as methyl cellosolve, cellosolve, isopropyl cellosolve, butyl cellosolve, diethylene glycol and monobutyl ether; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate, butyl acetate, ethyl propionate and cellosolve acetate; hydrocarbons such as hexane, octane, petroleum ether, cyclohexane, benzene, toluene and xylene; halogenated hydrocarbons such as carbon tetrachloride, trichloroethylene and tetrabromoethane; ethers such as ethyl ether, dimethyl glycol and trioxane tetrahydrofuran; acetals such as methylal and diethyl acetal; organic acids such as formic acid, acetic acid and propionic acid; and sulfur- or nitrogen-containing organic compounds such as nitropropene, nitrobenzene, dimethylamine, monoethanolamine, pyridine, dimethyl sulfoxide and dimethyl formamide. Two or more of any of these solvents may also be used in the form of a mixture. With respect to the solvent, the monomer may be in a concentration of from 1 to 80% by weight, and preferably from 10 to 65% by weight.
The polymeric dispersion stabilizer used in the process for production the toner of the present invention, any known compound may be used. As specific examples, it may include polystyrene; polystyrene derivatives such as poly-p-hydroxystyrene and polystyrene sulfonic acid; and polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyvinyl alcohol, polyvinyl alkyl ethers, polyvinyl acetal, polyvinyl carboxylic acid, polyacrylamide, polymethacrylamide, polyacrylonitrile, polyvinyl pyridine, polyvinyl pyrrolidone, polyvinyl imidazole, polyethyleneimine, poly-2-alkyl-oxazolines, polyvinyl formamide, polyethylene, polypropylene, polyvinyl chloride, polydimethylsiloxane, polyoxyalkylene and cellulose derivatives. Two or more kinds of polymeric dispersion stabilizers may simultaneously be used, or may be used in the form of a copolymer.
As a particularly preferred embodiment, the polymeric dispersion stabilizer may be a polymer or random copolymer containing at least one of structural repeating units represented by the following Formulas (3) to (5). This is especially effective for the property of incorporating the pigment, and brings about an improvement in coloring power of the toner and a dramatic improvement in pigment incorporation efficiency. 
The polymeric dispersion stabilizer may preferably have a number-average molecular weight of from 5,000 to 50,000. If it has a number-average molecular weight larger than 50,000, the reaction medium may have so high a viscosity as to tend to make particle size distribution non-uniform. If on the other hand it has a number-average molecular weight smaller than 5,000, its dispersion stabilization effect may be obtained with difficulty, making it difficult to obtain a product having good particle size distribution.
The polymeric dispersion stabilizer may also preferably be in a concentration of from 0.1 to 50% by weight, and more preferably from 0.1 to 30% by weight, based on the weight of the solvent.
The polymerization initiator used in the process for producing the toner of the present invention may include known polymerization initiators. Stated specifically, it may include azo compounds such as 2,2xe2x80x2-azobisisobutyronitrile, 2,2xe2x80x2-azobis-(2,4-dimethylvaleronitrile), 2,2xe2x80x2-azobis(2-methylbutyronitrile), 1,1xe2x80x2-azobis-(cyclohexane-1-carbonitrile), dimethyl-2,2xe2x80x2-azobisisobutyrate, 4,4xe2x80x2-azobis-4-cyanovaleronitrile and 2,2xe2x80x2-azobis(4-methoxy-2,4-dimethylvaleronitrile); peroxides such as benzoyl peroxide, and methyl ethyl ketone peroxide; nucleophilic reagents such as alkali metals, metal hydroxides and Grignard reagents; and protonic acid, metal halides and stabilized carbonium ions. The polymerization initiator may preferably be in a concentration of from 0.1 to 20% by weight, and more preferably from 0.1 to 10% by weight, based on the weight of the monomer.
In the case when the toner of the present invention is produced by polymerization, a chain transfer agent may be used, which may include known chain transfer agents.
In the present invention, toner additives as shown below may further be used in order to provide the toner with various properties.
In order to stabilize triboelectric charging performance of the toner, a charge control agent may be incorporated in the toner particles. In this case, it is preferable to use a charge control agent having a high toner charging speed and capable of maintaining a constant charge quantity stably. When the polymerization method is used to produce the toner particles, charge control agents having no polymerization inhibitory action are particularly preferred. Stated specifically, as negative charge control agents, preferred are metal compounds of salicylic acid, alkyl salicylic acids, dialkyl salicylic acids, naphthoic acid or dicarboxylic acids, polymer type compounds having sulfonic acid or carboxylic acid in the side chain, boron compounds, urea compounds, silicon compounds and carixarene. As positive charge control agents, preferred are quaternary ammonium salts, polymer type compounds having such a quaternary ammonium salt in the side chain, guanidine compounds, and imidazole compounds. Any of these charge control agents may preferably be added in a amount of from 0.5 to 10 parts by weight based on 100 parts by weight of the binder resin.
Additives such as a fluidity-providing agent, an abrasive, a lubricant and charge controlling particles may also externally be added to the toner particles.
As the fluidity-providing agent, metal oxides such as silicon oxide, aluminum oxide and titanium oxide may preferably be used. These may more preferably be those having been subjected to hydrophobic treatment. As the abrasive, metal oxides such as cerium oxide, aluminum oxide, magnesium oxide and chromium oxide, nitrides such as silicon nitride, carbides such as silicon carbide, and metal salts such as strontium titanate, calcium sulfate, barium sulfate and calcium carbonate may preferably be used. As the lubricant, fluorine resin powders such as vinylidene fluoride and polytetrafluoroethylene, and fatty acid metal salts such as zinc stearate and calcium stearate may preferably be used. As the charge controlling particles, metal oxides such as tin oxide, titanium oxide, zinc oxide, silicon oxide and aluminum oxide, and carbon black may preferably be used.
Any of these external additives may be used in an amount of from 0.1 part to 10 parts by weight, and preferably from 0.1 part to 5 parts by weight, based on 100 parts by weight of the toner particles. These additives may be used alone or in combination of two or more types. The toner of the present invention may be toner particles themselves, or may be toner particles to which any of the additives have been added.
The toner of the present invention may be used as a one-component developer, or may be blended with a carrier so as to be used as a two-component developer.
Triboelectric charge quantity of the toner used in the present invention is measured by a method described below.
The toner and the carrier are blended in a suitable blend quantity (2 to 15% by weight) when made into a developer, and are blended with a Turbula mixer for 180 seconds. This blended powder (developer) is put in a container made of a metal at the bottom of which a conductive screen of 635 meshes is provided, and then sucked by means of a suction device. The triboelectric charge quantity of the toner is determined from the difference in weight before and after the suction and from the potential accumulated in a capacitor connected to the container. Here, suction pressure is set at 250 mmHg. By this method, the triboelectric charge quantity (Q) is calculated according to the following expression.
xe2x80x83Q(xcexcC/g)=(Cxc3x97V)/(W1xe2x88x92W2)
wherein W1 is the weight before suction, W2 is the weight after suction, C is the capacity of the capacitor, and V is the potential accumulated in the capacitor.